1. Field of the Invention
The present invention relates in general to electrical signal relays and in particular to a relay assembly having a low profile and a short signal path for use in routing high frequency signals to automated test equipment.
2. Description of Related Art
The present invention relates to a low-profile relay assembly suitable for use in switching high frequency signals in automated testing and other applications. For example the relay assembly may be used to switch between various inputs of a high-frequency digitizer or to connect various channels of an integrated circuit tester to input/output terminals of a high-frequency integrated circuit device under test (DUT). In high-frequency test applications, we want to position the test circuit that communicates with the DUT as close as possible to the DUT to minimize the distance signals must travel between the DUT and the test circuits. Short signal paths help to minimize time delays and signal distortion. Since a relay occupies space, we increase the signal path distance between a test circuit and a DUT when we insert a relay in that path. Thus we would like to make a relay as short as possible in the direction of signal flow though the relay.
A typical integrated circuit tester includes a separate digital tester channel connected to each terminal of a DUT, with each channel either transmitting a test signal to the DUT terminal or receiving a test signal from the DUT terminal. An IC tester may also include one or more parametric test units (PMUs) for conducting analog tests on various terminals of a DUT. Thus the IC tester must be able to switch the DUT terminal between its digital test channel and a PMU. High frequency IC testers typically use relays rather than transistor switches to perform this switching function because relays do not distort signals as much as transistor switches. Transmission lines that connect transistor and relay switches include stubs that cause further signal distortion, and transistor switches also exhibit leakage and other undesirable signal path characteristics that compromise test accuracy. Since a tester may need hundreds of channels to test a large DUT, since we want to position each channel""s digital drivers and receivers as close as possible to the DUT, and since we have to place relays between those drivers and receivers and the DUT, we would like to be able to pack a large number of relays into a relatively small space near the DUT. Thus in this IC tester application, we not only want to use relays having relatively short signal paths, we also want to use relays that don""t require very much space in directions perpendicular to those signal paths so that we can pack a large number of them into a relatively small three-dimensional space.
A typical magnetic reed relay employed in integrated circuit tester applications because of its small size includes a coil of wire surrounding a pair of contact fingers. When a current passes through the coil, it produces a magnetic flux that moves the contact fingers together or apart to make or break the relay contact. In order to produce a sufficiently large magnetic flux without requiring a large current the coil must have many turns. This multiple-turn coil adds width to a coil and makes it difficult to pack a large number of coils into a small area.
A relay assembly in accordance with the invention implementing a set of relays includes a chassis and a signal board mounted within the chassis. Each relay includes a control rod slideably mounted within the chassis above the signal board, a resilient contact arm mounted on the signal board below the control arm, and a coil assembly mounted adjacent to a magnetic end of the control rod. A separate spring is positioned between each control rod and the chassis so that it normally forces the control rod to slide in a direction away from the coil assembly. However when a current is applied to the coil assembly it produces a magnetic flux attracting the magnetic end of the control rod toward the coil assembly. As it moves toward the coil assembly, the control rod presses down on the relay""s contact arm causing it to contact a pad on the surface of the signal board, thereby creating a signal path through the relay arm between two points on the signal board. When the coil current is turned off, the spring pushes the control rod away from the coil assembly so that it no longer presses on the relay arm. The relay arm thereupon breaks its contact with the pad.
In accordance with another aspect of the invention conductors on the signal board route signals from the relay contacts to the circuits that transmit and receive signals through the relay contact arms.
In accordance with a further aspect of the invention, integrated circuits that transmit and receive signals via the relay contact arms are mounted on the signal board proximate to the contacts so as to minimize signal path distance.
It is an object of the invention to provide a relay assembly that concentrates many relays into a small volume.
It is another object of the invention to provide a relay assembly providing relays with very short signal paths through their contacts.
It is a further object of the invention to provide a relay assembly providing relay contacts that can be positioned very close to devices that communicate via the relays.
The concluding portion of this specification particularly points out and distinctly claims the subject matter of the present invention. However those skilled in the art will best understand both the organization and method of operation of the invention, together with further advantages and objects thereof, by reading the remaining portions of the specification in view of the accompanying drawing(s) wherein like reference characters refer to like elements.